July 24, 2012
From Jennifer Grant, NYS IPM Program with contributions from Keith Waldron:
Many of you saw or heard about the massive invasion of true armyworm across New York in early June. Now the 2nd generation of those invaders is here.
Last week our field crops colleagues reported small caterpillars (1/8th to ½ inch) in grass hayfields in western, northern and eastern New York. Although I have yet to hear any reports of this generation infesting turf, I am sure they are out there. Be especially vigilant of turfgrass that was infested by the first generation of armyworm, and turf in rural areas where wheat, hay and corn are commonly grown.
Young caterpillars skeletonize leaves, whereas older ones will eat the entire blade. If populations are allowed to build, feeding can produce circular bare areas in fine turfgrass. Birds are important armyworm predators so the presence of birds might indicate an armyworm infestation.
Monitor for armyworms by using a disclosing solution (soap flush). Mix 1-2 tablespoons of liquid dish soap into a gallon of water, and pour onto turf until the soil is saturated. Wait 5-10 minutes to see larvae that climb to the top of leaf blades to escape the irritation of the soap. True armyworm are nocturnal, so sampling for them very early or late in the day may yield better results. There is no agreed upon threshold, but I have seen guidelines ranging from 1-10/ft2. If natural enemies such as tachinid fly parasites, and fungal and viral diseases are detected, higher numbers can be tolerated.
If potentially damaging populations are detected, treatment while larvae are still small is most effective. As described last month, good low impact insecticides to use include spinosad, Bt, or any labeled pyrethroid. Endophyte-enhanced grasses, and turf previously treated with preventative grub control products should be protected. Low mowing of turf, especially if done at night, will provide some mechanical destruction of caterpillars.